Packet loss occurs frequently in VoIP or wireless voice communication systems. Lost packets result in clicks or pops or other artifacts that greatly degrade the perceived speech quality at the receiver side. To combat the adverse impact of packet loss, packet loss concealment (PLC) algorithms, also known as frame erasure concealment algorithms, have been described. Such algorithms normally operate at the receiver side by generating a synthetic audio signal to cover missing data (erasures) in a received bit stream. Among various PLC methods, time domain pitch-based waveform substitution, such as G.711 Appendix I (ITU-T Recommendation G.711 Appendix I, “A high quality low complexity algorithm for packet loss concealment with G.711,” 1999, which is incorporated by reference), may be used. However, these approaches degrade audio quality notably in the event of consecutive packet loss, often generating artifacts due to the repetition of similar content over several frames or due to low signal periodicity.
PLC in the time domain typically cannot be directly applied to decoded speech which has been determined from a transform domain codec due to an extra aliasing buffer. For this purpose, PLC schemes in the transform domain, e.g. in the MDCT domain, have been described. However, such schemes may cause “robotic” sounding artifacts and may lead to rapid quality degradation, notably if PLC is used for a plurality of lost packets.
Therefore, there is a need to improve audio quality by mitigating artifacts through advanced PLC algorithms used in conjunction with transform domain codecs.